1. Field of the Invention
The present invention relates to a feed horn structure for receiving satellite communications, specifically, satellite broadcastings, and manufacturing method thereof, a converter with the feed horn structure, and a satellite communications receiving antenna.
2. Description of the Background Art
FIG. 11 is a perspective view of a satellite broadcasting receiving antenna. Radio waves from a satellite are reflected at a parabola antenna 150 and enter a feed horn 101 and guided. The radio waves thus guided are converted by a converter 140 connected to feed horn 101 into television signals or audio signals (e.g., Japanese Patent Laying-Open No. 7-38321, Japanese Patent Laying-Open No. 9-46102, Japanese Utility Model Laying-Open No. 6-81120).
FIG. 12 is a front view of a feed horn structure with a horn cap, showing their vertical cross section, in a conventional LNB (Low Noise Block down) converter. FIG. 13 is a cross sectional view of the feed horn structure above along the line XIII—XIII in FIG. 12. As shown in FIGS. 12 and 13, conventionally, feed horn 101 and horn cap 102 are removable from each other, and forming the feed horn structure when combined together. Of these feed horn structure elements, the horn cap must be formed with a material “transparent” to radio waves that does not attenuate incidental radio waves, i.e., must be formed with a non-conductive material, as a minimum requirement. As for the feed horn, since it serves as a waveguide tube, at least the inner surface thereof must be formed with a conductor. To this end, both of the parts are conventionally manufactured separately as separate members and combined together at an assembly step. In the assembly step, a plurality of hooks 103 provided on the horn cap are mated with feed horn 101, and thus they are combined.
According to the combining method above, the balance of the mating force may be disturbed, resulting in generation of whitening or crack near the hooks of the horn cap. Additionally, since an O ring 104 is used to maintain the airtightness, the cost is increased.
Therefore, there has been a need for a feed horn structure that combines the feed horn and the horn cap without employing the structure such as the above mentioned hooks yielding large stress concentration.